Summary                                                                             .                                       
      
      In many citrus areas around the world the California red scale (CRS) Aonidiella aurantii (Hemiptera: Diaspididae) is considered a key pest. In eastern Spain it has spread during the last decades up to cover a vast extension of citrus landscapes. The chemical control of CRS is difficult, and is frequently followed by recurrent infestations in a short period, the appearance of resistance to different products used for its control and the elimination of natural enemies present in the field. The improvement of integrated pest management and biological control techniques for CRS requires the knowledge of the natural enemy species composition in each climatic zone, their seasonal fluctuation in abundance, parasitism and predatory levels, how they distribute in the plant, and how they are affected by the climate.
      Although much has been studied in laboratory about the Aphytis (Hymenoptera: Aphelinidae) parasitoids, the main control agents of CRS,  it is still not well-known which combination of natural enemies achieves better host control in the field, how parasitism rate varies along the year or how parasitoids distribute and compete in the field in relation to climate. The action of Aphytis, ectoparasitoids, is complemented in many citrus areas by the endoparasitoids Comperiella bifasciata (Hymenoptera: Encyrtidae) and Encarsia perniciosi (Hymenoptera: Aphelinidae) which can parasitize different scale instars than Aphytis species. Very little is known about the fitness and the biological responses under different climate conditions of these endoparasitoids. Similarly, the impact of predators on the scale population has been rarely studied.
      Currently, in Eastern Spain, A. melinus, an introduced species and the superior competitor, has displaced the native parasitoid Aphytis chrysomphali from hot and dry areas (inland and southern areas) as it can better tolerate summer hot temperatures. However, in contrast to what it happens in most citrus areas around the world, both A. melinus and A. chrysomphali coexist along the coast. The relative abundance of A. chrysomphali increases from south to north, being in higher percentage in the northern areas where summer is milder. Declining temperatures during autumn and winter have a greater negative effect on A. melinus than A. chrysomphali, since the indigenous A. chrysomphali is more cold-tolerant and better adapted to these weather conditions. The negative effect of winter temperatures on A. melinus allows the earlier use of the available host resource in late winter and spring by A. chrysomphali and the coexistence of both parasitoids in the same orchard via temporal niche partitioning, being A. melinus more abundant during the summer. In addition, as both parasitoids prefer different red scale instars for parasitism (smaller for A. chrysomphali) its combination in the field could result in a better CRS control. We demonstrate the role of spatiotemporal weather conditions and seasonal changes in host stages on the variation of parasitoids relative abundance and coexistence.
      The parasitoids E. perniciosi and Aphytis lingnanensis were found only in a coastal semitropical area (La Marina) being the former the most abundant (13% of the total parasitoids found). The parasitoids of A. aurantii show different scale instars and different periods of the year as preferred for parasitism. Aphytis melinus parasitized more young females whereas A. chrysomphali preferred second instar stages and E. perniciosi highly parasitized scale molts and gravid females that are not parasitizable by Aphytis. In the orchards where A. melinus was present in high numbers, either alone or coexisting with A. chrysomphali, parasitism rates were higher (average 22.4%) than in the orchards where A. chrysomphali was the dominant parasitoid (average 11.5%). The levels of parasitism by Aphytis spp. were highest between August and November and lowest in February and March. The annual average parasitism rate by E. perniciosi was 12.3%, reaching the highest levels during the spring. Scales on fruits were more preferred for parasitism by Aphytis than those on twigs whereas E. perniciosi parasitized more scales on twigs. The best parasitism level was achieved when the ectoparasitoids A. melinus and A. chrysomphali occurred together with the endoparasitoid E. perniciosi. The reason was that they complement each other on controlling the different parts of the tree, the different CRS stages and the different seasons of the year. The average annual mortality rate of A. aurantii was 73.6%. The analysis of dead scales killed by Aphytis confirmed the results obtained in parasitism of live scales. The most abundant predators were Lestodiplosis aonidiellae (Diptera: Cecidomyiidae) and Rhyzobius lophantae (Coleoptera: Coccinellidae). Predators had much lower incidence on CRS populations than parasitoids but high effect on controlling mobile crawlers and mature female scales, showing the importance of keeping a high natural enemy complex in the field for a good control of the pest.
      Slight differences in winter and summer temperatures or humidity conditions between contiguous Mediterranean ecosystems are responsible of large variations in parasitoid species composition emphasizing the importance of considering temperature and humidity at different levels besides the optimal. Introductory releases of C. bifasciata achieved the establishment in groves placed in the inland citrus area whereas E. perniciosi and A. lingnanensis established only in the semitropical area. Experiments in laboratory, to complement field results, determined the decisive influence on the introduced parasitoids C. bifasciata and E. perniciosi of the extreme climatic conditions that occur naturally. The highest rm values for C. bifasciata and E. perniciosi were reached at temperature-humidity regimes typical from inland and subtropical citrus areas respectively, the same areas in which releases of these parasitoids achieved their establishment. The longevity of both species at different temperature-humidity conditions also reflected their adaptability to dry or humid areas. These results, together with the rm values obtained by other authors on Aphytis species and their field distribution, demonstrate that the study of life-history traits and the rm of parasitoids under different temperature-humidity conditions constitute a valid method to predict the potential areas of establishment and distribution of newly introduced insects. Previous unsuccessful releases and the distribution of CRS parasitoids in different citrus areas around the world can be explained through the rm of these insects at different temperature-humidity regimes.